At home, I run my MacBook in clamshell mode (closed lid, external display).

This works fine when you're connected to the power adapter, but it doesn't work when running on battery. That's how it's supposed to be and Apple has some kb entry on the issue. But it's also lame.

You can prevent the machine from sleeping when closed by running InsomniaX, but then it'll assume the builtin display is still active, so you end up with a two-display setup when you really only want the external. This is obviously less than ideal.

So, is there any work around, hack, utility, black magic that I can use to make it run in clamshell mode while strictly on battery power?

Also, bonus points for a solution that makes the AC status not affect the machine state at all. (Like, you know, it does normally, when not in clamshell.)

2 Answers
2

If you haven't done so already, attach the external screen, keyboard
and mouse.

Press a key on the keyboard (like Shift) and click the mouse once.

Close the lid and wait for the Macbook to go to sleep.

While sleeping, click the external mouse once, the Macbook will
wake up.

If all goes well, the external screen
will display the Dock and menu-bar
after a few seconds. As soon as you
see this, the Apple logo on the
Macbook shouldn't light up, open the
lid of the Macbook. The Macbook won't
go to sleep, won't power up its
built-in screen and you can now use
clamshell mode in lid-open mode.

EDIT: See comments on this post for kch's experiences with this method.

Also, using InsomniaX worked. I did the steps as described, after that loaded and enabled InsomniaX and closed the lid. And here I am typing this comment, with external screen in lovely full resolution.
–
kchJul 31 '09 at 4:52

Well, this does seem to be the only way. I'm accepting this answer, would appreciate if you could update it with my InsomniaX comment.
–
kchAug 10 '09 at 17:12

maybe things have changed in the four years since this was posted, or maybe I'm doing something wrong, but this isn't working for me...
–
KipSep 7 '13 at 18:56

I've written an answer that incorporates kch's InsomniaX suggestion and preserves full screen resolution, but does require an initial plug in to stop the system sleeping whilst the lid goes down. The benefit is the MacBook screen goes off, which doesn't happen on a normal lid-close with InsomniaX preventing sleep.